1. Field of the Invention
The present invention relates to syringes and more particularly concerns syringe assemblies having needle isolation features.
2. Description of Related Information
Generally speaking, a hypodermic syringe consists of a cylindrical barrel, most commonly made of plastic or glass, with a distal end adapted to be connected to a hypodermic needle and a proximal end adapted to receive a stopper or plunger rod assembly. One of the purposes of the stopper is to provide a relatively air-tight seal between itself and the syringe barrel so that the movement of the stopper up and down the barrel will cause liquid, blood or other fluids to be drawn into or forced out of the syringe through the distal end.
A wide variety of injectable medications are prefilled in syringe barrel assemblies by pharmaceutical manufacturers, contract packagers, hospital pharmacies and the like. Medication contained in these syringes may sit for many weeks or months before administration of the medication to the patient. Under these circumstances, it is desirable to isolate the medication from the environment as thoroughly as possible. This task is more easily accomplished at the proximal end of the syringe where, a resilient rubber stopper can effectively seal the barrel. At the distal end of the syringe barrel, the problem of isolating the medication from the environment is more difficult to solve. In rigid barrel syringes, without hypodermic needles attached, it is common practice to seal the tip at the distal end of the syringe with elastomeric tip caps such as described in U.S. Pat. No. 4,444,310 where the tip cap is removed at the time of use and the hypodermic needle assembly is placed on the syringe tip. This type of tip cap works very well but requires the installation of a hypodermic needle at the time of use. Also, this type of tip cap does not discourage or prevent reuse of the syringe barrel.
Another method of sealing the distal end of the syringe, having a hypodermic needle attached, is through the use of a needle shield having a resilient element which seals the distal end of the needle as taught in U.S. Pat. No. 4,986,818. This method of sealing also works very well but may not be desirable where contact between the liquid medication and the needle cannula during storage is not desirable. Also, needle shields of this type do not prevent or discourage reuse of the syringe.
The art has recognized the use of hypodermic syringes for the efficient storage and delivery of liquid medication and has provided structure for sealing the distal end of the syringe barrel which has been proven over time to be efficacious. However, there is still a need for simple prefillable syringe device which combines all of the delivery and storage advantages of prior art hypodermic syringes but with the ability to store medication without contact with a needle cannula and to prevent refilling of the syringe through the syringe tip after the contents of the syringe have been expelled.